The club had revealed yesterday via a short statement that the former England boss was travelling to Finch Farm to complete the formalities of his contract and he then attended last night's game against his old club, West Ham, from the Directors' Box at Goodison Park.
The arrangement represents an apparent compromise between the two parties, with Allardyce agreeing to a shorter 18-month term than the three years he was reportedly after when he first discussed succeeding Ronald Koeman last month.
Everton, meanwhile, are believed to be paying him £6m a year, a substantial increase on the £2.5m annual salary he was on at Crystal Palace last season.
“I'm delighted to confirm Sam as our new manager," major shareholder Farhad Moshiri said. "His strong leadership will bring great motivation and get the best out of players.
“Sam understands the long-term ambitions we have for this great club and I know he is a man who gives it his all and is focused 24 hours a day on the club."
Allardyce, meanwhile, called for unity and commitment from the squad following the Toffee's dreadful start to the season.
“Let's try to get a healthy spirit around the club,” he said. “I think that whatever's happened before we've just got to all rally around. Because we are all in it together and let's all pull in the same direction.
“We have to give the players every possibility to play to their best, really give them no excuses for not playing to their best and get them right back up to the top level we believe they're capable of.
“Peter Reid is one of my best mates, so are Andy Gray and Paul Bracewell, whom I worked with at Sunderland. These people have always made me aware of just how special and unique a club Everton is and I feel really enthused and energised to come in as manager.”
Known as the man struggling clubs turn to steer them away from relegation, Allardyce has successfully ensured the Premier League safety of , Crystal Palace, West Ham, Sunderland and Blackburn Rovers in recent years after initially making his name at Bolton Wanderers.
Though he has become synonymous with the English northwest, he was born and raised in Dudley in the West Midlands before getting his start in football as a player with the Trotters in the 1970s.
His first managerial assignment was also in the northwest with Blackpool before he moved to Notts County, the only club to date where he has overseen relegation, although he was hired too late to save them from the drop to Division Three.
After joining Bolton, he led them to the Premier League and eventually into European competition via a sixth-place finish but left in 2007. A stint at Newcastle followed before he was brought in at Ewood Park, Upton Park, the Stadium of Light and then Selhurst Park to bring stability and order to struggling teams seemingly headed for relegation from the top flight.
Though his achievements at Bolton remain the pinnacle of his managerial career thus far, Allardyce's biggest appointment prior to the Everton job was that of England manager last year.
Hired to replace Roy Hodgson, it was an opportunity he hoped would allow him to dispel his image as a "fire-fighter" and manage at the top of the game. His spell lasted just one match, however, as he was sacked following a sting by the Telegraph in which he was recorded apparently negotiating with an undercover reporter posing as a Far Eastern businessman looking to pay money for help in skirting Fifa's third-party ownership rules of players.
Having rehabilitated his image somewhat when he was taken on by Palace, he elected to retire from the game when they parted company at the end of last season but he has now answered the call from Farhad Moshiri and the Everton board to try and stabilise what has been a chaotic 2017-18 season at Goodison.
His first match in charge will be against Huddersfield Town this weekend. Caretaker boss David Unsworth steps back down to the Under-23s having overseen eight matches that included two wins, two defeats and a draw in the Premier League and three defeats in cup competition.